1. Field of the Invention
The present invention relates generally to the functionalization of nanotubes in order to enhance various properties of the nanotubes including solubility in solvents. More particularly, the present invention is directed to the noncovalent functionalization of nanotubes by treating them with certain types of polymers that wrap around the nanotubes.
2. Description of Related Art
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference. For convenience, the reference materials are numerically referenced and grouped in the appended bibliography.
The small dimensions and remarkable physical properties of single-walled carbon nanotubes (SWNTs) render them unique materials with a wide range of potential applications.1 However, their lack of solubility in solvents presents a considerable impediment toward harnessing their applications.2 Although the covalent functionalization of the sidewalls of SWNTs leads to soluble samples and opens up the possibility of attaching other molecules to nanotubes,3,4 all the covalent chemical approaches disrupt the extended π-networks on their surfaces, diminishing both their mechanical and electronic properties. On the other hand, a noncovalent supramolecular approach which involves polymer wrapping5-8 of the nanotubes preserves their unique properties.
The creation of polymer-nanotube composites holds out much promise, both for reinforcing the polymers and extending their applications in electronic device settings. Recently, such a scenario has been demonstrated5 in the case of the conjugated luminescent polymer, poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]} (PmPV), filled with either SWNTs or multi-walled carbon nanotubes. Compared with the pristine polymer, these nanotube/PmPV composites have exhibited large increases (by nearly eight orders of magnitude) in electrical conductivity with little loss in photoluminescence and electroluminescence yields. Moreover, the composite is far more robust than the polymer on its own when it comes to mechanical strength and photo-bleaching properties. The coiled morphologies of the polymer chains help them wrap themselves around the nanotubes when they are suspended in dilute solutions of the polymer.
We have also reported7 on the use of PmPV for wrapping around SWNTs. Complexes (SWNT/PmPV) are formed on account of stabilizing noncovalent bonding interactions, presumably as a result of π—π stacking and van der Waals interactions between PmPV and the surfaces of the SWNTs. The nature of the interaction of PmPV, as well as that of poly{(2,6-pyridinylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]} (PPyPV) 1), with SWNTs has been investigated and compared.8 Optoelectronic devices have also been fabricated with these complexes. It is clear that noncovalent functionalization of carbon nanotubes can be achieved without disrupting the primary structure of the nanotubes themselves. To this extent, noncovalent functionalization has potentially a virtue that all forms of covalent functionalization lack.